This invention relates to a surface acoustic wave transducer, and more particularly pertains to such transducer which includes an apodized counter electrode of an improved configuration.
FIG. 1 illustrates a typical example of the conventional surface acoustic wave transducers employing a piezoelectric thin film. On a non-piezoelectric substrate 1 such as glass, is deposited interdigital electrodes 2 of a vacuum evaporated A1 which is shaped by a photolithography. A piezoelectric thin film 3 is laid over on the interdigital electrodes 2. On the piezoelectric thin film 3 is provided a counter electrode 4 which has an outline of a form corresponding to a desired apodized function.
The counter electrode 4 is made of a vacuum evaporated A1 and is shaped by the photolithography process. In the photolithography process therefor, it is necessary to precisely align a mask for forming the counter electrode 4 with the interdigital electrodes 2.
However, it has been difficult to perform such mask-alignment always with sufficient precision in a manufacturing process. The incomplete mask-alignment causes the dispersion of the relative location between the interdigital electrodes 2 and the counter electrode 4, resulting in dispersion of the amplitude characteristic and the phase characteristic of the manufactured surface acoustic wave transducer.